(Reuters) - Online rental marketplace Airbnb will address reports of widespread racial discrimination against non-white guests by displaying photos less prominently on its website, promoting instant bookings and changing some of its technology, according to a report commissioned by the company.

The report, released on Thursday, followed months of criticism of Airbnb, sparked partly by comments under Twitter hashtag #AirbnbWhileBlack about discrimination against black people.

"Bias and discrimination have no place on Airbnb, and we have zero tolerance for them," Chief Executive Officer Brian Chesky wrote in an email to users. "Unfortunately, we have been slow to address these problems, and for this I am sorry."

Before the end of the year, Airbnb will roll out changes to its reservation request system that emphasize trip details, reviews and verified IDs while testing various formats that downplay users' photos, said the report from Laura Murphy & Associates.

San Francisco-based Airbnb will also expand its instant book program, which allows guests who meet preferences preset by hosts to make reservations without prior approval, to 1 million of its 2 million listings by January.

Under that program, hosts can require guests to provide Airbnb with government issued ID or have or a 4.5 out of 5 star rating to be approved for booking. Hosts can also cancel bookings without paying a fee if they have issues with guests' behavior.

The company will also implement technology that prevents hosts from booking new guests if they tell another guest their listing is unavailable for the same time frame.

The company will make its anti-bias training program available online and will highlight hosts who participate. Anti-bias training is mandatory for all staff.

The company has also introduced hiring rules designed to increase diversity among senior-level positions and is retraining customer service representatives on its diversity policy.

The changes received mixed reviews from civil rights organizations and other critics.

Rashad Robinson, executive director of anti-discrimination organization Color of Change, called Airbnb's plans a victory for activists and individuals who sparked the protests.

Earlier this year Color of Change sent a letter to Airbnb executives demanding they take action to address discrimination complaints.

However, Lawyer's Committee for Civil Rights Under Law President Kristen Clarke said creating a policy eliminating the use of photos altogether prior to booking would have made the greatest difference.

"The company's reliance on photos prior to the confirmation stage will allow discrimination to continue rearing its ugly head," said Clarke, a former Airbnb guest who penned a New York Times op-ed piece discussing her experience with discrimination on the site.

Rohan Gilkes, a tech entrepreneur who cofounded vacation rentals site Innclusive in June as a response to discrimination complaints on Airbnb, said the report also fails to address discrimination based on guests' names.

In the report, Murphy called profile photos "essential to Airbnb's overall mission" to build communities and said technological fixes were the best course of action.

"Technology can bring us together and technology shouldn't ask us to hide who we are," reads the report.

(Reporting by Deborah M. Todd; Editing by Lisa Von Ahn and David Gregorio)